Cylinders of an engine may be selectively deactivated to conserve fuel. For example, four cylinders of an eight cylinder engine may be deactivated while at the same time the four remaining cylinders continue to operate. Deactivating four of eight cylinders increases the efficiency of the active cylinders while reducing engine pumping losses. One way to deactivate an engine cylinder is to cease fuel flow to the cylinder and hold a cylinder's intake and exhaust valves in a closed position during an engine cycle. The engine may continue to rotate without pumping air through the deactivated cylinder. The cylinder may be reactivated by injecting fuel to the cylinder and restarting opening and closing of the cylinder's intake and exhaust valves. However, it may be possible that a cylinder does not properly reactivate after it has been deactivated. For example, the cylinder's intake and/or exhaust valves may remain closed as the engine rotates. Consequently, the engine may not have its full rated power and engine emissions may degrade if the inactive cylinder is not detected.
The inventors herein have recognized that an engine's exhaust valves may remain closed over an engine cycle after the exhaust valves have been commanded to operate and have developed an engine operating method, comprising: commanding reactivation of a cylinder that is deactivated; and adjusting engine operation in response to an oxygen concentration in an engine intake manifold being less than a threshold oxygen concentration.
By recognizing that intake manifold oxygen concentration may be indicative of exhaust valve operation, it may be possible to adjust engine operation so that engine emission degradation may be reduced. For example, a position of an EGR valve may be adjusted to compensate for additional EGR that may enter the engine's intake valve via one or more cylinders having exhaust valves that remain closed when they are commanded to operate. Further, intake manifold oxygen concentration may a basis for distinguishing a portion of cylinders that were deactivated and operate as desired from a portion of cylinders that were deactivated and do not operate as is desired. In particular, intake manifold oxygen concentration may be evaluated when a fraction of deactivated cylinders is reactivated while the remaining deactivated cylinders remain inactive. If the intake manifold oxygen concentration is not reduced to less than a threshold oxygen concentration, it may be determined that the cylinders that were reactivated include exhaust valves that operate as desired. The cylinders having properly operating exhaust valves may be reactivated so as to provide and increased amount of engine torque as compared to when all deactivated cylinders remain in a deactivated state. The remaining portion of cylinders may remain deactivated so that internal EGR may be limited. In this way, the engine torque capacity may be increased without having to activate cylinders that include degraded exhaust valve operation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.